Hepatitis

Common Types of Hepatitis Viruses

An Overview of Viral Hepatitis

When we speak of hepatitis, we most often refer to the viral form of the disease. The term hepatitis, by definition, is simply the inflammation of the liver which can be caused by any number of conditions, including direct organ damage, exposure to chemicals and toxins, bacterial or parasitic infections, and autoimmune disease.

Viral hepatitis is by far the most common type of hepatitis in the world, caused by a variety of unrelated viruses, each which behave similarly but have characteristics all their own.

These characteristics include:

  • Modes of transmission (how the virus is spread)
  • Pathogenesis (how the disease progresses)
  • Symptomatology (what and when symptoms commonly appear)
  • Rates of morbidity (illness) and mortality (death)

There are five common types of viral hepatitis—classified alphabetically from hepatitis A through E—that are distributed either worldwide or to specific parts of the world. Two other nominal types (hepatitis F and GB) have also been classified as possible causes, although scientists are still debating their existence.

While there are other viruses that can cause liver inflammation (including the Epstein Barr virus and certain herpes simplex viruses), hepatitis A through E are the types we most commonly refer to as being the causes of viral hepatitis.

In total, hepatitis A through E account for nearly 1.3 million deaths per year. Of these, hepatitis B and C are considered to be at global epidemic scale, with more infections and deaths each year than HIV, tuberculosis, and malaria combined.

Hepatitis A

Hepatitis A is caused by the hepatitis A virus (HAV) and is commonly spread by ingesting HAV-infected feces either through water or food contamination or from person to person (including during sex).

Under-cooked shellfish is a common source of disease transmission.

The time between infection and the appearance of symptoms is around two to six weeks, although many will experience no symptoms at all. When symptoms do appear, they tend to last for around eight weeks on average and can include such tell-tale signs as:

  • Nausea
  • Vomiting
  • Diarrhea
  • Fever
  • Abdominal pain
  • Extreme tiredness
  • Yellowing of the skin and eyes (jaundice)
  • Darkening of the urine
  • Pale, clay-colored stools

There is no specific treatment for hepatitis A as symptoms tend to resolve on their own. Once infected, a person is immune for life. Death is considered uncommon, although some elderly people may be at increased risk for acute liver failure (usually those with pre-existing liver disease).

An HAV vaccine is widely available—delivered by injection over two courses—which can protect against infection for 15 years or more.

Hepatitis B

Hepatitis B is caused by the hepatitis B virus (HBV) and is primarily spread by infected blood or body fluids or passed from mother to child during pregnancy.

Injecting drug use and sexual intercourse are common routes of transmission.

Hepatitis B can present with acute (self-limiting) symptoms during the early stage of infection, although some will have no symptoms at all. These early stage symptoms are similar to those of hepatitis A and typically appear within 30 to 80 days of exposure.

Once acute symptoms resolved, the virus can persist for many years during the chronic (long-lasting) stage of infection. It is during this period that persistent inflammation can lead to changes in the liver that gradually damage the architecture of the organ itself.

While many people will remain asymptomatic during chronic infection, the disease can progress silently over the course of years in others. Scarring of the liver (fibrosis) can gradually build over 10 to 20 years, eventually leading to a condition called cirrhosis in which the liver is less able to function. Liver failure and liver cancer are both complications associated with advanced HBV infection.

While the majority of people with hepatitis B will spontaneously clear the virus soon after infection, those with chronic infection can be treated to reduce the risk of cirrhosis and cancer.  Currently, there are seven drugs licensed for use in HBV therapy. And while the drugs cannot clear the virus itself, they can effectively suppress viral replication, thereby reducing liver inflammation.

An HBV vaccine is also available—which is delivered by injection over three courses—as well as a combination vaccine able to prevent both hepatitis A and B.

Hepatitis C

Hepatitis C is caused by the hepatitis C virus (HCV) and is spread primarily through injecting drug use. Transmission from mother to child during pregnancy is also common as is sexual transmission of the virus (most predominantly among gay or bisexual men co-infected with HIV).

In some less developed parts of the world, hepatitis C is commonly transmitted through unsterile injections and medical procedures, and even in tattoo or shaving parlors where tools have been tainted with another patron’s blood.

Like hepatitis B, hepatitis C can present with acute symptoms during early stage infection, typically six to eight weeks after exposure. Most will spontaneously clear the virus within 60 days, often with no symptoms (or even awareness) of infection.

In those unable to achieve clearance, around 10 to 15 percent will advance to cirrhosis within 20 to 30 years. Of these, 20 to 25 percent will experience decompensated cirrhosis (wherein the liver is unable to function) or liver cancer, both of which carry a greater than 50 percent risk of mortality.

The introduction of newer direct-acting antivirals (DAAs) has greatly improved outcomes for people with chronic HCV infection, with some drugs boasting cure rates of more than 95 percent (even in those with advanced cirrhosis).

According to the World Health Organization (WHO), an estimated 300 million people are infected with HCV worldwide, resulting in nearly 700,000 deaths from cirrhosis and liver cancer each year. There is currently no vaccine to prevent hepatitis C infection.

Hepatitis D

Hepatitis D is caused by the hepatitis D virus (HDV) and can only cause disease if co-occurring with the hepatitis B virus (HBV). The route of transmission is, therefore, the same as HBV as are the symptoms and the disease itself, albeit far more severe.

In fact, a person co-infected with HBV and HDV has a high risk of experiencing liver failure during the acute stage of infection, with a more rapid progression to cirrhosis during chronic infection. Rates of liver cancer are also increased.

As a result, HBV/HDV co-infection is known to have the highest rate of mortality of all viral types. There are currently few treatment options known to be effective in controlling the hepatitis D virus. However, HBV vaccination can protect against hepatitis D since the virus is wholly dependent on hepatitis B to replicate.  

While hepatitis D is considered rare in the U.S., it is known to be widely distributed in West Africa, South America, Central America, Russia, Central Asia, the Pacific Islands, and the Mediterranean.

Hepatitis E

Hepatitis E is caused by the hepatitis E virus (HEV) and, like hepatitis A, is commonly spread through the fecal-oral route. The average time between infection and the appearance of symptoms is around three to six weeks, although many will experience no symptoms at all. When symptoms do appear, they will be similar to those of hepatitis A and last for up to eight weeks.

Recovery from symptoms tends to lead to viral clearance in almost all infected. Among the few who progress to chronic infection, illness is typically limited in those with compromised immune systems (such as people with advanced HIV infection or organ transplants). Pregnant women are also at increased risk of liver failure, typically during the third trimester of pregnancy.

The use of the drug ribavirin has been shown to achieve viral clearance in around 65 percent of chronically infected individuals. Unlike hepatitis A, however, there is no vaccine for hepatitis E. Considered rare in the U.S., hepatitis E is predominately distributed in Central Asia, although outbreaks have been noted in Central America, Sub-Saharan Africa, and the Middle East.

Sources:

World Health Organization (WHO). "What is hepatitis?" Geneva, Switzerland; online Q&A reviewed July 2016.

Centers for Disease Control and Prevention (CDC). "Viral Hepatitis" Atlanta, Georgia; August 14, 2016.

American Association for the Study of Liver Disease (AASLD). "Assessing the Global and Regional Burden of Liver Disease." Washington, D.C.; press release issued November 3, 2013.

American Association for the Study of Liver Diseases (AASLD) and the Infectious Diseases Society of America (IDSA). "HCV Guidance: Recommendations for Testing, Managing, and Treating Hepatitis C." Updated July 6, 2016.

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